To transmit user data to a Base Station (BS) in a mobile communication system, a UE employs a procedure for receiving an uplink grant from the BS (i.e. uplink scheduling). Two uplink scheduling schemes are available in a mobile communication system, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE).
One of the uplink scheduling schemes is that a UE transmits a Scheduling Request (SR) signal to a BS on a Physical Uplink Control CHannel (PUCCH) and the BS grants data transmission of the UE on a Physical Uplink Shared CHannel (PUSCH). The other uplink scheduling scheme is that a BS periodically transmits an UpLink Grant (ULG) signal to a UE, thereby granting data transmission of the UE on a PUSCH.
FIG. 1 illustrates an uplink scheduling scheme based on a ULG signal transmitted by a BS in a cellular communication system.
Referring to FIG. 1, a BS 100 periodically transmits a ULG signal to a UE 102 in block 104 and the UE 102 transmits data to the BS 100 on a PUSCH in block 106.
In the ULG-based uplink scheduling scheme, even in the absence of user data to be transmitted to the BS, the UE that has received a ULG signal and has been allocated to the PUSCH generates a Medium Access Control (MAC) Protocol Data Unit (PDU) padded with zeroes at a MAC layer. The zero-padded MAC PDU is created by padding meaningless information (e.g. ‘0s’) to a MAC Service Data Unit (SDU). This MAC PDU is subjected to a data process including Hybrid Automatic Repeat reQuest (HARQ) processing, channel coding (e.g. turbo coding), control information multiplexing, channel interleaving, and scrambling and is then transmitted over the air in Orthogonal Frequency Division Multiplexing (OFDM) based on Single Carrier-Frequency Division Multiple Access (SC-FDMA) at a physical layer.
Even though the zero-padded MAC PDU carries meaningless data, the UE performs the data process at the MAC layer and the physical layer. The resulting increase in the computation volume of a data processor (e.g. an LTE MODEM) increases the computation resource waste and power consumption of the UE. Transmission of a zero-padded MAC PDU causes severe problems to a UE having limited resources and power, particularly a Software Defined Radio (SDR) UE having all functions of a MODEM implemented in software.